Composite and method of manufacturing the same

ABSTRACT

Provided is a nanotube-polymer composite which can effectively utilize characteristics of a carbon nanotube structure. The composite includes a carbon nanotube structure and a polymer, in which: the carbon nanotube structure has a network structure constructed by mutually cross-linking functional groups bonded to multiple carbon nanotubes through chemical bonding of the functional groups together; and the polymer is filled in the network structure. Also provided is a method of manufacturing a composite which includes the steps of: supplying a base body surface with a solution containing multiple carbon nanotubes to which multiple functional groups are bonded; mutually cross-linking the multiple carbon nanotubes through chemical bonding of the multiple functional groups together to construct a network structure constituting a carbon nanotube structure; impregnating the network structure with a polymer liquid forming a polymer; and combining the carbon nanotube structure and the polymer by curing the polymer liquid.

FIELD OF THE INVENTION AND RELATED ART STATEMENT

The present invention relates to a composite of a carbon nanotubestructure and a polymer that are combined (hereinafter, may be referredto as a nanotube-polymer composite) and a method of manufacturing thesame.

Carbon nanotubes (CNTs), with their unique shapes and characteristics,may find various applications. A carbon nanotube has a tubular shape ofone-dimensional nature which is obtained by rolling one or more graphenesheets composed of six-membered rings of carbon atoms into a tube. Acarbon nanotube formed from one graphene sheet is called a single-wallcarbon nanotube (SWNT) while a carbon nanotube formed from multiplegraphene sheets is called a multi-wall carbon nanotube (MWNT). SWNTs areabout 1 nm in diameter whereas multi-wall carbon nanotubes are severaltens nm in diameter, and both are far thinner than their predecessors,which are called carbon fibers.

One of the characteristics of carbon nanotubes resides in that theaspect ratio of length to diameter is very large since the length ofcarbon nanotubes is on the order of micrometers. Carbon nanotubes areunique in their extremely rare nature of being both metallic andsemiconductive because six-membered rings of carbon atoms in carbonnanotubes are arranged into a spiral. In addition, the electricalconductivity of carbon nanotubes is very high and allows a current flowat a current density of 100 MA/cm² or more.

Carbon nanotubes excel not only in electrical characteristics but alsoin mechanical characteristics. That is, the carbon nanotubes aredistinctively tough, as attested by their Young's moduli exceeding 1TPa, which belies their extreme lightness resulting from being formedsolely of carbon atoms. In addition, the carbon nanotubes have highelasticity and resiliency resulting from their cage structure. Havingsuch various and excellent characteristics, carbon nanotubes are veryappealing as industrial materials.

Applied researches that exploit the excellent characteristics of carbonnanotubes have been heretofore made extensively. To give a few examples,a carbon nanotube is added as a resin reinforcer or as a conductivecomposite material while another research uses a carbon nanotube as aprobe of a scanning probe microscope. Carbon nanotubes have also beenused as minute electron sources, field emission electronic devices, andflat displays. An application that is being developed is to use a carbonnanotube as a hydrogen storage.

As described above, carbon nanotubes may find use in variousapplications and have been recently used as a filler for a polymer resinused in various materials. Various fillers heretofore have been added toa polymer for imparting functions such as electrical conductivity,physical strength, and flame retardance.

An electrically conductive filler such as carbon black, carbon fibers,or metal oxides has been mixed with a polymer such as polycarbonate orwith an elastomer such as butadiene rubber for imparting electricalconductivity, for example. Increasing an amount of an electricallyconductive material mixed for imparting high electrical conductivity hascaused problems including deterioration of moldability and significantdeterioration of physical characteristics such as impact strength.

A vapor grown carbon fibers, a carbon nanotube, or the like has beenrecently mixed with a resin for solving such problems (see JP 07-102112A, for example).

A carbon nanotube has higher electrical conductivity compared to that ofa conventional carbon-based electrically conductive filler. A carbonnanotube also has a high aspect ratio and easily forms a networkstructure in a resin, and thus is very fine and includes many carbonnanotubes form per unit weight. Thus, mixing of a carbon nanotube with aresin in an amount comparable to that of the conventional carbon-basedelectrically conductive filler provides a resin composition havinghigher electrical conductivity.

However, the carbon nanotubes form an aggregate or entanglement in theresin through the above method, and the method had problems that uniformdispersion of the nanotubes and increase in a filling amount (density)of the nanotubes are difficult. As a result, problems arouse in thatelectrical conductivity was not uniform, and that a resin compositionhaving stable electrical conductivity could not be obtained.

SUMMARY OF THE INVENTION

The present invention has been made to solve the above problems of theprior art and specifically provides a nanotube-polymer composite whichcan effectively utilize characteristics of a carbon nanotube.

In order to solve the above problems, a composite of the presentinvention includes a carbon nanotube structure and a polymer, in which:the carbon nanotube structure has a network structure constructed bymutually cross-linking functional groups bonded to multiple carbonnanotubes through chemical bonding of the functional groups together;and the polymer is filled in the network structure.

The carbon nanotube structure has a network structure consisting solelyof carbon nanotubes, that is, mutually cross-linked carbon nanotubes. Acomposite is formed by impregnating the network structure of the carbonnanotubes with a polymer liquid and curing the polymer liquid. Thus, anetwork of the carbon nanotubes is assuredly formed in the polymer, anda resin composition having stable electrical conductivity can beobtained.

The nanotube-polymer composite of the present invention employs a carbonnanotube structure in which multiple carbon nanotubes construct anetwork structure through multiple cross-linked sites. As a result,unlike the case where carbon nanotubes are merely filled in a polymer,stable electrical characteristics and mechanical characteristics areprovided regardless of a contact state of entanglement of the carbonnanotubes. Further, localization of the nanotubes in the composite dueto easily caused aggregation of the separated nanotubes and lowdispersion is prevented, thereby providing a more homogeneous structure.As a result, an effect of filling the carbon nanotubes can be providedmore uniformly.

According to the present invention, the polymer may include variousresins such as polyethylene, polypropylene, polyvinyl chloride,polyamide, polyimide, and an epoxy resin.

Among the polymers, an elastomer such as butadiene rubber, acrylicrubber, or isoprene rubber is preferable in view of ease ofprocessability, effect of enhancing mechanical strength of thecomposite, and affinity with the carbon nanotubes.

The carbon nanotube structure is preferably obtained by curing asolution containing multiple carbon nanotubes to which multiplefunctional groups are bonded, to thereby form a cross-linked sitethrough chemical bonding of the multiple functional groups bonded to thecarbon nanotubes.

Of those, a preferable first structure for the cross-linked site has astructure constructed by cross-linking the multiple functional groupstogether through a cross-linking agent in the solution, and thecross-linking agent is more preferably not self-polymerizable.

By forming the carbon nanotube structure through the above curing of thesolution, the cross-linked site where the carbon nanotubes arecross-linked together has a cross-linking structure in which residues ofthe functional groups remaining after a cross-linking reaction areconnected together using a connecting group which is a residue of thecross-linking agent remaining after the cross-linking reaction.

If the cross-linking agent has a property of polymerizing with othercross-linking agents (self-polymerizability), the connecting group maycontain a polymer in which two or more cross-linking agents areconnected, thereby reducing an actual density of the carbon nanotubes inthe carbon nanotube structure. Therefore, sufficient electricalconductivity and mechanical strength may not be provided as anelectrically conductive material.

On the other hand, a non self-polymerizable cross-linking agent allowscontrol of a gap between each of the carbon nanotubes to a size of across-linking agent residue used. Therefore, a desired network structureof carbon nanotubes can be obtained with high duplicability. Further,reducing the size of the cross-linking agent residue can extremelynarrow a gap between each of the carbon nanotubes electrically andphysically. In addition, carbon nanotubes in the structure can bedensely structured.

Therefore, a non self-polymerizable cross-linking agent can provide thecarbon nanotube structure according to the present invention exhibitingthe electrical characteristics and physical characteristics of a carbonnanotube itself at high levels.

In the present invention, the term “self-polymerizable” refers toproperty with which the cross-linking agents may prompt a polymerizationreaction with each other in the presence of other components such aswater or in the absence of other components. On the other hand, the term“not self-polymerizable” means that the cross-linking agent has no suchproperty.

A selection of a non self-polymerizable cross-linking agent as thecross-linking agent provides a cross-linked site, where carbon nanotubesin the composite of the present invention are cross-linked together,having primarily an identical cross-linking structure. Furthermore, theconnecting group preferably has hydrocarbon as its skeleton, and thehydrocarbon preferably has 2 to 10 carbon atoms. Reducing the number ofcarbon atoms can shorten the length of a cross-linked site andsufficiently narrow a gap between carbon nanotubes as compared to thelength of a carbon nanotube itself. As a result, a carbon nanotubestructure having a network structure composed substantially only ofcarbon nanotubes can be obtained.

Examples of the functional group include —OH, —COOH, —COOR (where Rrepresents a substituted or unsubstituted hydrocarbon group), —COX(where X represents a halogen atom), —NH₂, and —NCO. As election of atleast one functional group from the group consisting of the abovefunctional groups is preferable, and in such a case, a cross-linkingagent, which may prompt a cross-linking reaction with the selectedfunctional group, is selected as the cross-linking agent.

Further, examples of the preferable cross-linking agent include apolyol, a polyamine, a polycarboxylic acid, a polycarboxylate, apolycarboxylic acid halide, a polycarbodiimide, and a polyisocyanate. Aselection of at least one cross-linking agent from the group consistingof the above cross-linking agents is preferable, and in such a case, afunctional group, which may prompt a cross-linking reaction with theselected cross-linking agent, is selected as the functional group.

At least one functional group and at least one cross-linking agent arepreferably selected respectively from the group consisting of thefunctional groups exemplified as the preferable functional groups andthe group consisting of the cross-linking agents exemplified as thepreferable cross-linking agents, so that a combination of the functionalgroup and the cross-linking agent may prompt a cross-linking reactionwith each other.

Examples of the particularly preferable functional group include —COOR(where R represents a substituted or unsubstituted hydrocarbon group).Introduction of a carboxyl group into carbon nanotubes is relativelyeasy, and the resultant substance (carbon nanotube carboxylic acid) hashigh reactivity. Therefore, after the formation of the substance, it isrelatively easy to esterify the substance to convert its functionalgroup into —COOR (where R represents a substituted or unsubstitutedhydrocarbon group). The functional group easily prompts a cross-linkingreaction and is suitable for formation of a carbon nanotube structure.

A polyol can be exemplified as the cross-linking agent corresponding tothe functional group. A polyol is cured by a reaction with —COOR (whereR represents a substituted or unsubstituted hydrocarbon group), andforms a robust cross-linked substance with ease. Among polyols, each ofglycerin and ethylene glycol reacts with the above functional groupswell. Moreover, each of glycerin and ethylene glycol itself is highlybiodegradable, and provides a low environmental load.

In the cross-linked site where multiple carbon nanotubes are mutuallycross-linked, the functional group is —COOR (where R represents asubstituted or unsubstituted hydrocarbon group). The cross-linked siteis —COO(CH₂)₂OCO— in the case where ethylene glycol is used as thecross-linking agent. In the case where glycerin is used as thecross-linking agent, the cross-linked site is —COOCH₂CHOHCH₂OCO— or—COOCH₂CH(OCO—)CH₂OH if two OH groups contribute to the cross-linking,and the cross-linked site is —COOCH₂CH(OCO—)CH₂OCO— if three OH groupscontribute to the cross-linking. The chemical structure of thecross-linked site may be any chemical structure selected from the groupconsisting of the above four structures.

A second structure preferable as the structure of the cross-linked siteof carbon nanotubes is a structure formed through chemical bonding ofmultiple functional groups together. More preferably, a reaction thatforms the chemical bonding is any one of dehydration condensation, asubstitution reaction, an addition reaction, and an oxidative reaction.

The carbon nanotube structure of this case forms a cross-linked site bychemically bonding together functional groups bonded to the carbonnanotubes, to thereby form a network structure. Therefore, the size ofthe cross-linked site for bonding the carbon nanotubes together becomesconstant depending on the functional group to be bonded. Since a carbonnanotube has an extremely stable chemical structure, there is a lowpossibility that functional groups or the like other than a functionalgroup to modify the carbon nanotube are bonded to the carbon nanotube.In the case where the functional groups are chemically bonded together,the designed structure of the cross-linked site can be obtained, therebyproviding a homogeneous carbon nanotube structure.

Furthermore, the functional groups are chemically bonded together, sothat the length of the cross-linked site between the carbon nanotubescan be shorter than that in the case where the functional groups arecross-linked together with a cross-linking agent. Therefore, the carbonnanotube structure is dense, and an effect peculiar to a carbon nanotubeis easily provided.

In addition, multiple carbon nanotubes construct a network structurethrough multiple cross-linked sites in the carbon nanotube structure ofthe present invention. As a result, excellent characteristics of acarbon nanotube can be stably used unlike a material such as a merecarbon nanotube dispersion film or resin dispersion film in which carbonnanotubes are only accidentally in contact with each other and aresubstantially isolated from each other.

The chemical bonding of the multiple functional groups together ispreferably one selected from —COOCO—, —O—, —NHCO—, —COO—, and —NCH— in acondensation reaction. The chemical bonding is preferably at least oneselected from —NH—, —S—, and —O— in a substitution reaction. Thechemical bonding is preferably —NHCOO— in an addition reaction. Thechemical bonding is preferably —S—S— in an oxidative reaction.

Examples of the functional group to be bonded to a carbon nanotube priorto the reaction include —OH, —COOH, —COOR (where R represents asubstituted or unsubstituted hydrocarbon group), —X, —COX (where Xrepresents a halogen atom), —SH, —CHO, —OSO₂CH₃, —OSO₂(C₆H₄)CH₃, —NH₂,and —NCO. It is preferable to select at least one functional group fromthe group consisting of the above functional groups.

Particularly preferable examples of the functional group include —COOH.A carboxyl group can be relatively easily introduced into a carbonnanotube. In addition, the resultant substance (carbon nanotubecarboxylic acid) has high reactivity, easily prompts a condensationreaction by using a dehydration condensation agent such asN-ethyl-N′-(3-dimethylaminopropyl)carbodiimide, and thus is suitable forforming a carbon nanotube structure.

The multiple carbon nanotubes are each particularly preferably amulti-wall carbon nanotube having high electrical conductivity forenhancing electrical conductivity of the nanotube-polymer composite andfor hardly deteriorating the characteristics of a carbon nanotubebecause an inner graphene sheet structure is destroyed only to a smallextent when functional groups are bonded.

(Manufacturing Method)

Next, a method of manufacturing a nanotube-polymer composite of thepresent invention includes the steps of: supplying a base body surfacewith a solution containing multiple carbon nanotubes to which multiplefunctional groups are bonded; mutually cross-linking the multiple carbonnanotubes through chemical bonding of the multiple functional groupstogether to construct a network structure constituting a carbon nanotubestructure; impregnating the network structure with a polymer liquid; andcombining the carbon nanotube structure and the polymer by curing thepolymer liquid.

According to the present invention, in the step of supplying the basebody surface with a solution containing carbon nanotubes to whichmultiple functional groups are bonded (hereinafter, simply referred toas “cross-linking solution” or “cross-linking application solution” insome cases), a structure (in the form of a film, a layer, a block, orthe like) is first formed with the cross-linking solution on theentirety or a part of the surface of the base body. Then, in thesubsequent cross-linking step, the thus supplied structure is cured toform a carbon nanotube structure in which the multiple carbon nanotubesare mutually cross-linked through chemical bonding of the multiplefunctional groups together to construct a network structure. The abovetwo steps can stabilize the structure itself of the carbon nanotubestructure on the surface of the base body.

Subsequently, the carbon nanotube structure and the polymer are combinedby impregnating the network structure of the carbon nanotube structurethus formed with the polymer liquid and curing the polymer liquid. Gapsin the network structure do not have to be completely filled with thepolymer, and a level of filling may be determined according to use.

An example of the impregnation method employed at this time is: a methodof impregnating specific portions through dropping, application, or thelike of a polymer liquid, or a method of dipping a base body supportinga carbon nanotube structure in a polymer liquid. Another example thereofis a method of dispersing a carbon nanotube structure itself in apolymer liquid after the carbon nanotube structure and the base body areseparated. The former method forms a composite in an area comparable toa surface area of the base body, and thus is suitable for formation of acomposite having a relatively small area. The latter method involvesdispersion of the carbon nanotube structure after the structure isseparated from the base body, and thus is suitable for formation of alarge composite.

Examples of the polymer include various resins such as polyethylene,polypropylene, polyvinyl chloride, polyamide, polyimide, and an epoxyresin.

Among the polymers, an elastomer such as butadiene rubber, acrylicrubber, or isoprene rubber is preferably used.

However, the polymer is selected in view of affinity between the carbonnanotube and the polymer. A surface of the carbon nanotube ishydrophobic, and thus a hydrophobic polymer is preferable. Specificexamples of the hydrophobic polymer include polyethylene, polypropylene,and polyvinyl chloride.

Next, a method of forming the carbon nanotube structure will bedescribed. In forming chemical bonding between functional groups, afirst method preferable for forming a cross-linked site is a method ofcross-linking the multiple functional groups with a cross-linking agentin the solution. More preferably, the cross-linking agent is notself-polymerizable.

In the method of manufacturing a nanotube-polymer composite of thepresent invention, examples of the functional groups for forming across-linked site by using a cross-linking agent include —OH, —COOH,—COOR (where R represents a substituted or unsubstituted hydrocarbongroup), —COX (where X represents a halogen atom), —NH₂, and —NCO. It ispreferable to select at least one functional group from the groupconsisting of the above functional groups. In such a case, across-linking agent, which may prompt a cross-linking reaction with theselected functional group, is selected as the cross-linking agent.

Further, preferable examples of the cross-linking agent include apolyol, a polyamine, a polycarboxylic acid, a polycarboxylate, apolycarboxylic acid halide, a polycarbodiimide, and a polyisocyanate. Itis preferable to select at least one cross-linking agent from the groupconsisting of the above cross-linking agents. In such a case, afunctional group, which may prompt a cross-linking reaction with theselected cross-linking agent, is selected as the functional group.

The at least one functional group and the at least one cross-linkingagent are preferably selected respectively from the group consisting ofthe functional groups exemplified as the preferable functional groupsand the group consisting of the cross-linking agents exemplified as thepreferable cross-linking agents, such that a combination of thefunctional group and the cross-linking agent thus selected may prompt amutual cross-linking reaction.

Particularly preferable examples of the functional group include —COOR(where R represents a substituted or unsubstituted hydrocarbon group). Acarboxyl group can be introduced into a carbon nanotube with relativeease, and the resultant substance (carbon nanotube carboxylic acid) hashigh reactivity. Therefore, it is relatively easy to esterify thesubstance to convert its functional group into —COOR (where R representsa substituted or unsubstituted hydrocarbon group) after the formation ofthe substance. The functional group easily prompts a cross-linkingreaction, and is suitable for the formation of a carbon nanotubestructure.

In addition, a polyol can be exemplified as the cross-linking agentcorresponding to the functional group. A polyol is cured by a reactionwith —COOR (where R represents a substituted or unsubstitutedhydrocarbon group) to easily form a robust cross-linked substance. Amongpolyols, each of glycerin and ethylene glycol reacts with the abovefunctional groups well. Moreover, each of glycerin and ethylene glycolitself is highly biodegradable, and provides a low environmental load.

Further, a second method for forming a cross-linked site is a method ofchemically bonding the multiple functional groups together.

By following the second method, the size of the cross-linked site forbonding the carbon nanotubes together becomes constant depending on thefunctional group to be bonded. Since a carbon nanotube has an extremelystable chemical structure, there is a low possibility that functionalgroups or the like other than a functional group to modify the carbonnanotube are bonded to the carbon nanotube. In the case where thefunctional groups are chemically bonded together, the designed structureof the cross-linked site can be obtained, thereby providing ahomogeneous carbon nanotube structure.

Furthermore, the functional groups are chemically bonded together, sothat the length of the cross-linked site between the carbon nanotubescan be shorter than that in the case where the functional groups arecross-linked together with a cross-linking agent. Therefore, the carbonnanotube structure is dense, and tends to readily provide an effectpeculiar to a carbon nanotube.

A reaction for chemically bonding the functional groups is particularlypreferably one of a condensation reaction, a substitution reaction, anaddition reaction, and an oxidative reaction.

The multiple carbon nanotubes to be used in the method of manufacturinga nanotube-polymer composite of the present invention are eachpreferably a multi-wall carbon nanotube having high electricalconductivity. This is because when functional groups are bonded, aninner graphene sheet structure is destroyed only to a small extent, andthus the characteristics of a carbon nanotube hardly deteriorate.

The present invention can provide the composite of the carbon nanotubeand the polymer having satisfactory mechanical characteristics peculiarto a carbon nanotube and having high electrical and thermalconductivity, thereby expanding the application of the nanotube-polymercomposite.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the present invention will be described indetail based on the following figures, wherein:

FIG. 1 is a schematic diagram showing a nanotube-polymer composite ofthe present invention;

FIG. 2 shows a reaction scheme for synthesis of carbon nanotubecarboxylic acid in (Addition Step) of Example 1;

FIG. 3 shows a reaction scheme for esterification in (Addition Step) ofExample 1; and

FIG. 4 shows a reaction scheme for cross-linking through an esterexchange reaction in (Cross-linking Step) of Example 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Hereinafter, each of a carbon nanotube-polymer composite and a method ofmanufacturing the carbon nanotube-polymer composite will be describedspecifically through the description of the embodiments of the presentinvention.

[Nanotube-polymer Composite]

A nanotube-polymer composite of the present invention includes a carbonnanotube structure having a network structure and a polymer filled inthe network structure. The nanotube-polymer composite may have twoforms: (1) a composite including as a filler multiple carbon nanotubestructures each having a network structure dispersed in a polymer; and(2) a composite including a polymer, having a comparable contour as acarbon nanotube structure, filled in the network structure of the carbonnanotubes. In the form (1), the carbon nanotube structures may besupported on a substrate, but in the form (2), the carbon nanotubestructure is preferably peeled off from a support substrate used duringmanufacture and then filled with the polymer. Hereinafter, the form (1)will be described mainly.

FIG. 1 shows a schematic diagram of a nanotube-polymer composite 10. Acarbon nanotube structure 1 is constructed by cross-linking multiplecarbon nanotubes 11, and cross-linked sites 12 connect togetherfunctional groups bonded to the carbon nanotubes through chemicalbonding, thereby forming a network structure. A region of the compositeencircled is shown in an enlarged schematic diagram. Note that, thefunctional groups are significantly small with respect to lengths of thecarbon nanotubes, and thus, the cross-linked portions cannot be visuallyobserved and the carbon nanotubes are close to each other. As a result,an arrangement of the carbon nanotubes maintains a stereoscopicconfiguration in the carbon nanotube structure 1, to thereby preventbundling and localization of the carbon nanotubes. Further, the carbonnanotubes are tough and flexible at the same time, and the carbonnanotube structure 1 mainly consisting of carbon nanotubes takes oversuch characteristics to serve as a flexible and tough filler. Acomposite material formed by dispersing such a carbon nanotube structure1 in a polymer 2 can provide a polymer having improved strength and acomposite having electrical or thermal conductivity of the carbonnanotubes.

<Polymer>

Examples of a polymer include various resins such as polyethylene,polypropylene, polyvinyl chloride, polyamide, polyimide, and an epoxyresin. Among the polymers, an elastomer such as butadiene rubber,acrylic rubber, or isoprene rubber is preferably used.

<Carbon Nanotube Structure>

In the present invention, the term “carbon nanotube structure” refers toa structure having a network structure constructed by mutuallycross-linking multiple carbon nanotubes. Provided that a carbon nanotubestructure can be formed in such a manner that carbon nanotubes aremutually cross-linked to construct a network structure, the carbonnanotube structure may be formed through any method. However, the carbonnanotube structure is preferably manufactured through a method ofmanufacturing a nanotube-polymer composite of the present inventiondescribed later for easy manufacture, a high-performancenanotube-polymer composite, and easy uniformization and control ofcharacteristics.

A first structure for the carbon nanotube structure employed as a fillerfor a nanotube-polymer composite described later is manufactured bycuring a solution (cross-linking solution) containing carbon nanotubeshaving functional groups and a cross-linking agent that prompts across-linking reaction with the functional groups, to prompt across-linking reaction between the functional groups of the carbonnanotubes and the cross-linking agent, to thereby form a cross-linkedsite. Furthermore, a second structure for the carbon nanotube structureis manufactured by chemically bonding together functional groups ofcarbon nanotubes to form cross-linked sites.

Hereinafter, the carbon nanotube structure in the nanotube-polymercomposite of the present invention will be described by way of examplesof the manufacturing method. Unless otherwise stated, the structures ofcross-linked sites are not considered.

(Carbon Nanotube)

Carbon nanotubes, which are the main component in the present invention,may be single-wall carbon nanotubes or multi-wall carbon nanotubes eachhaving two or more layers. Whether one or both types of carbon nanotubesare used (and, if only one type is used, which type is selected) may bedecided appropriately taking into consideration the use of thenanotube-polymer composite or the cost.

Carbon nanotubes in the present invention include ones that are notexactly shaped like a tube, such as: a carbon nanohorn (a horn-shapedcarbon nanotube whose diameter continuously increases from one endtoward the other end) which is a variant of a single-wall carbonnanotube; a carbon nanocoil (a coil-shaped carbon nanotube forming aspiral when viewed in entirety); a carbon nanobead (a spherical beadmade of amorphous carbon or the like with its center pierced by a tube);a cup-stacked nanotube; and a carbon nanotube with its outer peripherycovered with a carbon nanohorn or amorphous carbon.

Furthermore, carbon nanotubes in the present invention may include onesthat contain some substances inside, such as: a metal-containingnanotube which is a carbon nanotube containing metal or the like; and apeapod nanotube which is a carbon nanotube containing a fullerene or ametal-containing fullerene.

As described above, in the present invention, it is possible to employcarbon nanotubes of any form, including common carbon nanotubes,variants of the common carbon nanotubes, and carbon nanotubes withvarious modifications, without a problem in terms of reactivity.Therefore, the concept of “carbon nanotube” in the present inventionencompasses all of the above.

Those carbon nanotubes are conventionally synthesized through a knownmethod such as arc discharge, laser ablation, or CVD, and the presentinvention can employ any of the methods. However, arc discharge in amagnetic field is preferable from the viewpoint of synthesizing ahigh-purity carbon nanotube.

A diameter of carbon nanotubes used in the present invention ispreferably 0.3 nm or more and 100 nm or less. A diameter of the carbonnanotubes exceeding this upper limit undesirably results in difficultand costly synthesis. A more preferable upper limit of the diameter of acarbon nanotubes is 30 nm or less.

In general, the lower limit of the carbon nanotube diameter is about 0.3nm from a structural standpoint. However, too small a diameter couldundesirably lower the synthesis yield. It is therefore preferable to setthe lower limit of the carbon nanotube diameter to 1 nm or more, morepreferably 10 nm or more.

The length of carbon nanotubes used in the present invention ispreferably 0.1 μm or more and 100 μm or less. A length of the carbonnanotubes exceeding this upper limit undesirably results in difficultsynthesis or requires a special synthesis method raising cost. On theother hand, a length of the carbon nanotubes falling short of this lowerlimit undesirably reduces the number of cross-link bonding points percarbon nanotube. A more preferable upper limit of the carbon nanotubelength is 10 μm or less, and a more preferable lower limit of the carbonnanotube length is 1 μm or more.

The appropriate carbon nanotube content in the cross-linking solutionvaries depending on the length and thickness of carbon nanotubes,whether single-wall carbon nanotubes or multi-wall carbon nanotubes areused, the type and amount of functional groups in the carbon nanotubes,the type and amount of cross-linking agent or of an additive for bondingfunctional groups together, the presence or absence of a solvent orother additive used and, if one is used, the type and amount of thesolvent or additive, etc. The carbon nanotube content in the solutionshould be high enough to form a satisfactory carbon nanotube structureafter curing but not excessively high because the applicabilitydeteriorates.

Specifically, the ratio of carbon nanotubes to the entire cross-linkingsolution excluding the mass of the functional groups is 0.01 to 10 g/l,preferably 0.1 to 5 g/l, and more preferably 0.5 to 1.5 g/l, althoughthe ratio cannot be determined uniquely but is subject to variations asdescribed above.

The purity of the carbon nanotubes to be used is desirably raised bypurifying the carbon nanotubes before preparation of the cross-linkingsolution if the purity is not high enough. In the present invention, thehigher the carbon nanotube purity, the better the result can be.Specifically, the purity is preferably 90% or higher, more preferably95% or higher. Low purity causes the cross-linking agent to cross-linkwith carbon products such as amorphous carbon and tar, which areimpurities. This could change the cross-linking distance between carbonnanotubes, and desired characteristics may not be obtained. Apurification method for carbon nanotubes is not particularly limited,and any known purification method can be employed.

Such carbon nanotubes are used for the formation of a carbon nanotubestructure with predetermined functional groups added to the carbonnanotubes. A preferable functional group to be added at this time variesdepending on whether the carbon nanotube structure is formed through thefirst method or second method described above (a preferable functionalgroup in the former case is referred to as “Functional Group 1”, and apreferable functional group in the latter case is referred to as“Functional Group 2”).

How functional groups are introduced into carbon nanotubes will bedescribed in the section below titled (Method of Preparing Cross-linkingSolution).

Hereinafter, components that can be used for the formation of a carbonnanotube structure will be described for the respective first and secondmethods.

(Case of First Method)

In the first method in which a cross-linked site is formed using across-linking agent, carbon nanotubes can have any functional groups tobe connected thereto without particular limitations, as long asfunctional groups selected can be added to the carbon nanotubeschemically and can prompt a cross-linking reaction with any type ofcross-linking agent. Specific examples of such functional groups include—COOR, —COX, —MgX, —X (where X represents halogen), —OR, —NR¹R², —NCO,—NCS, —COOH, —OH, —NH₂, —SH, —SO₃H, —R″CH₂OH, —CHO, —CN, —COSH, —SR,—SiR′₃ (In the above formulae, R, R¹, R², R′, and R″ each independentlyrepresent a substituted or unsubstituted hydrocarbon group. R, R¹, R²,and R′ are each a monovalent hydrocarbon group and are each preferablyindependently selected from —C_(n)H_(2n−1) and —C_(n)H_(2n+1) (nrepresents an integer of 1 to 10). Of those, a methyl group or an ethylgroup is more preferable for each of R, R¹, R², and R′. R″ is a divalenthydrocarbon group and is preferably selected from —C_(n)H_(2n)— (nrepresents an integer of 1 to 10). Of those, a methylene group or anethylene group is more preferable for R″.). Note that the functionalgroups are not limited to those examples.

Of those, it is preferable to select at least one functional group fromthe group consisting of —OH, —COOH, —COOR (In the formulae, R representsa substituted or unsubstituted hydrocarbon group. R is preferablyselected from —C_(n)H_(2n−1) and —C_(n)H_(2n+1) (n represents an integerof 1 to 10). Of those, a methyl group or an ethyl group is morepreferable.), —COX (where X represents a halogen atom), —NH₂, and —NCO.In that case, a cross-linking agent, which can prompt a cross-linkingreaction with the selected functional group, is selected as thecross-linking agent.

In particular, —COOR (R is the same as that described above) isparticularly preferable. This is because a carboxyl group can beintroduced into a carbon nanotube with relative ease, because theresultant substance (carbon nanotube carboxylic acid) can be easilyintroduced as a functional group by esterifying the substance, andbecause the substance has good reactivity with a cross-linking agent.

R in the functional group —COOR is a substituted or unsubstitutedhydrocarbon group, and is not particularly limited. However, R ispreferably an alkyl group having 1 to 10 carbon atoms, more preferablyan alkyl group having 1 to 5 carbon atoms, and particularly preferably amethyl group or an ethyl group in terms of reactivity, solubility,viscosity, and ease of use as a solvent for a cross-linking solution.

The amount of functional groups introduced cannot be determined uniquelybecause the amount varies depending on the length and thickness of acarbon nanotube, whether the carbon nanotube is of a single-wall type ora multi-wall type, the type of a functional group, the use of thenanotube-polymer composite, etc. From the viewpoint of the strength ofthe cross-linked substance obtained, namely, the strength of the carbonnanotube structure, a preferable amount of functional groups introducedis large enough to add two or more functional groups to each carbonnanotube. How functional groups are introduced into carbon nanotubeswill be described in the section below titled [Method of ManufacturingNanotube-polymer Composite].

(Cross-linking Agent)

A cross-linking agent is an essential ingredient for the cross-linkingsolution. Any cross-linking agent can be used as long as thecross-linking agent is capable of prompting a cross-linking reactionwith the functional groups of the carbon nanotubes. In other words, thetype of cross-linking agent that can be selected is limited to a certaindegree by the types of the functional groups. In addition, theconditions of curing (heating, UV irradiation, visible lightirradiation, air setting, etc.) as a result of the cross-linkingreaction are naturally determined by the combination of thoseparameters.

Specific examples of the preferable cross-linking agent include apolyol, a polyamine, a polycarboxylic acid, a polycarboxylate, apolycarboxylic acid halide, a polycarbodiimide, and a polyisocyanate. Itis preferable to select at least one cross-lining agent from the groupconsisting of the above cross-linking agents. In that case, a functionalgroup which can prompt a reaction with the selected cross-linking agentis selected as the functional group.

At least one functional group and at least one cross-linking agent areparticularly preferably selected respectively from the group consistingof the functional groups exemplified as the preferable functional groupsand the group consisting of the cross-linking agents exemplified as thepreferable cross-linking agents, so that a combination of the functionalgroup and the cross-linking agent may prompt a cross-linking reactionwith each other. The following Table 1 lists the combinations of thefunctional group of the carbon nanotubes and the correspondingcross-linking agent, which can prompt a cross-linking reaction, alongwith curing conditions for the combinations.

TABLE 1 Functional group of carbon nanotube Cross-linking agent Curingcondition —COOR Polyol heat curing —COX Polyol heat curing —COOHPolyamine heat curing —COX Polyamine heat curing —OH Polycarboxylateheat curing —OH Polycarboxylic acid heat curing halide —NH₂Polycarboxylic acid heat curing —NH₂ Polycarboxylic acid heat curinghalide —COOH Polycarbodiimide heat curing —OH Polycarbodiimide heatcuring —NH₂ Polycarbodiimide heat curing —NCO Polyol heat curing —OHPolyisocyanate heat curing —COOH Ammonium complex heat curing —COOHcis-platin heat curing *R represents a substituted or unsubstitutedhydrocarbon group *X represents a halogen

Of those combinations, preferable is the combination of —COOR (where Rrepresents a substituted or unsubstituted hydrocarbon group and ispreferably selected from —C_(n)H_(2n−1) and —C_(n)H_(2n+1) (n representsan integer of 1 to 10). Of those, a methyl group or an ethyl group ismore preferable.) with good reactivity on the functional group side anda polyol, a polyamine, an ammonium complex, congo red, and cis-platin,which form a robust cross-linked substance with ease. The terms“polyol”, “polyamine”, and “ammonium complex” as used in the presentinvention are genetic names for organic compounds each having two ormore OH groups, NH₂ groups, and ammonium groups, respectively. Of those,one having 2 to 10 (more preferably 2 to 5) carbon atoms and 2 to 22(more preferably 2 to 5) OH groups is preferable in terms ofcross-linkability, solvent compatibility when an excessive amountthereof is charged, treatability of waste liquid after a reaction byvirtue of biodegradability (environmental suitability), yield of polyolsynthesis, and so on. In particular, the number of carbon atoms ispreferably lower within the above range because a gap between carbonnanotubes in the resultant carbon nanotube structure can be extremelynarrowed to bring the carbon nanotubes into substantial contact witheach other (to bring the carbon nanotubes close to each other).Specifically, glycerin and ethylene glycol are particularly preferable,and one or both of glycerin and ethylene glycol are preferably used as across-linking agent.

From another perspective, the cross-linking agent is preferably a nonself-polymerizable cross-linking agent. In addition to glycerin andethylene glycol as examples of the polyols mentioned above, butenediol,hexynediol, hydroquinone, and naphthalenediol are obviously nonself-polymerizable cross-linking agents. More generally, a prerequisitefor the non self-polymerizable cross-linking agent is to be without apair of functional groups, which can prompt a polymerization reactionwith each other, in itself. On the other hand, examples of aself-polymerizable cross-linking agent include one that has a pair offunctional groups, which can prompt a polymerization reaction with eachother (alkoxide, for example), in itself.

According to a method of manufacturing a nanotube-polymer composite ofthe present invention, the first method may involve: further including asolvent in the solution used in the supplying step and containing themultiple carbon nanotubes to which the functional groups are bonded andthe cross-linking agent; and supplying the base body surface with theresultant solution. The cross-linking agent may also serve as thesolvent depending on the type of the cross-linking agent.

Formation of a carbon nanotube structure only involves: supplying thebase body surface with the multiple carbon nanotubes to which functionalgroups are bonded and the cross-linking agent (the supplying step in themethod of manufacturing a nanotube-polymer composite of the presentinvention); and chemically bonding the functional groups together toform a cross-linked site (the cross-linking step in the method ofmanufacturing a nanotube-polymer composite of the present invention). Insupplying the base body surface with the multiple carbon nanotubes towhich functional groups are bonded and the cross-linking agent, the basebody surface is preferably supplied with a solution (cross-linkingsolution) containing the carbon nanotubes, the cross-linking agent, anda solvent. In particular, the solution is preferably applied as across-linking application solution to form a cross-linked substancefilm, for a simple, low cost operation in a short period of time.

(Case of Second Method)

In the second method, a cross-linked site of a carbon nanotube structureis formed by mutually cross-linking multiple functional groups bonded tocarbon nanotubes each having at least one different end through chemicalbonding of the functional groups, to thereby construct a networkstructure. The functional groups to be bonded to the carbon nanotubesare not particularly limited as long as the functional groups can bechemically added to the carbon nanotubes and is capable of reacting witheach other using some type of additive.

Specific examples of the functional group include —COOR, —COX, —MgX, —X(where X represents a halogen), —OR, —NR¹R², —NCO, —NCS, —COOH, —OH,—NH₂, —SH, —SO₃H, —R″CH₂OH, —CHO, —CN, —COSH, —SR, —SiR′₃ (In the aboveformulae, R, R¹, R², R′, and R″ each independently represent asubstituted or unsubstituted hydrocarbon group. R, R¹, R², and R′ areeach a monovalent hydrocarbon group and are preferably independentlyselected from —C₂H_(2n−1) and —C_(n)H_(2n+1) (n represents an integer of1 to 10). Of those, a methyl group or an ethyl group is more preferablefor each of R, R¹, R², and R′. R″ is a divalent hydrocarbon group and ispreferably selected from —C_(n)H_(2n)— (n represents an integer of 1 to10). Of those, a methylene group or an ethylene group is more preferablefor R″.). However, the functional group is not limited to those.

A reaction for chemically bonding the functional groups together isparticularly preferably dehydration condensation, a substitutionreaction, an addition reaction, or an oxidative reaction. The functionalgroups preferable for the respective reactions out of the abovefunctional groups are exemplified below.

According to the method of manufacturing a nanotube-polymer composite ofthe present invention, the second method may involve: preparing a supplysolution (cross-linking solution) used in the supplying step byincluding the multiple carbon nanotubes having the functional groupsbonded and the additive as required in a solvent; and supplying the basebody surface with the resultant solution.

When the reaction for chemically bonding the functional groups togetheris dehydration condensation, a condensation agent is preferably added asthe additive. Specific examples of preferable condensation agentsinclude an acid catalyst and a dehydration condensation agent such assulfuric acid, N-ethyl-N′-(3-dimethylaminopropyl)carbodiimide, anddicyclohexyl carbodiimide. It is preferable to select at least onecondensation agent from the group consisting of the above. In that case,the functional groups, which can prompt a reaction among the functionalgroups with the help of the selected condensation agent, are selected asthe functional groups.

The functional groups to be used in dehydration condensation arepreferably at least one functional group selected from the groupconsisting of —COOR (R represents a substituted or unsubstitutedhydrocarbon group and is preferably selected from —C_(n)H_(2n−1) and—C_(n)H_(2n+1) (n represents an integer of 1 to 10). Of those, a methylgroup or an ethyl group is more preferable.), —COOH, —COX (where Xrepresents a halogen atom), —OH, —CHO, and —NH₂.

Examples of the functional group particularly preferable for use indehydration condensation include —COOH. Introduction of a carboxyl groupinto carbon nanotubes is relatively easy, and the resultant substance(carbon nanotube carboxylic acid) has high reactivity. Therefore,functional groups for forming a network structure can be easilyintroduced into multiple sites of one carbon nanotube. Moreover, thefunctional group is suitable for formation of a carbon nanotubestructure because the functional group is easily subjected todehydration condensation. If the functional group to be used indehydration condensation is —COOH, sulfuric acid,N-ethyl-N′-(3-dimethylaminopropyl)carbodiimide, and dicyclohexylcarbodiimide described above are particularly preferable condensationagents.

When the reaction for chemically bonding the functional groups togetheris a substitution reaction, a base is preferably added as the additive.A base that can be added is not particularly limited, and may be anybase as long as the base is selected according to the acidity of ahydroxyl group.

Specific preferable examples of the base include sodium hydroxide,potassium hydroxide, pyridine, and sodium ethoxide. It is preferable toselect at least one base from the group consisting of the above bases.In that case, functional groups, which can prompt a substitutionreaction among the functional groups with the help of the selected base,are selected as the functional groups. In addition, the functionalgroups at this time are preferably at least one functional groupselected from the group consisting of —NH₂, —X (where X represents ahalogen atom), —SH, —OH, —OSO₂CH₃, and —OSO₂(C₆H₄)CH₃.

When the reaction for chemically bonding the functional groups togetheris an addition reaction, an additive is not always necessary. Thefunctional groups at this time are preferably —OH and/or —NCO.

When the reaction for chemically bonding the functional groups togetheris an oxidative reaction, an additive is not always necessary either.However, an oxidative reaction accelerator is preferably added as theadditive. An example of the oxidative reaction accelerator that can besuitably added is iodine. In addition, the functional groups at thistime are preferably —SH.

Further, it is also possible to bond a molecule, which partiallycontains those functional groups, with the carbon nanotubes to bechemically bonded at a preferable functional group portion exemplifiedabove. Even in this case, a functional group with a large molecularweight to be bonded to the carbon nanotubes is bonded as intended,enabling control of a length of the cross-linked site.

In chemically bonding the functional groups together, an additive thatcan form the chemical bonding among the functional groups can be used.Any additive that is capable of causing the functional groups of thecarbon nanotubes to react with each other can be used as such anadditive. In other words, the type of additive that can be selected islimited to a certain degree by the types of the functional groups andthe reaction. In addition, the conditions of curing (heating, UVirradiation, visible light irradiation, air setting, etc.) as a resultof the reaction are naturally determined by the combination of thoseparameters.

It is preferable to select at least two functional groups from the groupconsisting of the functional groups exemplified as preferable functionalgroups so that a combination of the selected functional groups iscapable of prompting a mutual reaction. Table 2 below lists functionalgroups (A) and (B) of carbon nanotubes capable of prompting a mutualcross-linking reaction and the names of corresponding reactions.

TABLE 2 Functional Functional group of carbon group of carbon Bondingsite nanotube(A) nanotube (B) Reaction —COOCO— —COOH — Dehydrationcondensation —S—S— —SH — Oxidative reaction —O— —OH — Dehydrationcondensation —NH—CO— —COOH —NH₂ Dehydration condensation —COO— —COOH —OHDehydration condensation —COO— —COOR —OH Dehydration condensation —COO——COX —OH Dehydration condensation —CH═N— —CHO —NH₂ Dehydrationcondensation —NH— —NH₂ —X Substitution reaction —S— —SH —X Substitutionreaction —O— —OH —X Substitution reaction —O— —OH —OSO₂CH₃ Substitutionreaction —O— —OH —OSO₂(C₆H₄)CH₃ Substitution reaction —NH—COO— —OH—N═C═O Addition reaction *R represents a substituted or unsubstitutedhydrocarbon group *X represents a halogen

Formation of a carbon nanotube structure only involves: supplying thebase body surface with the multiple carbon nanotubes to which functionalgroups are bonded and the additive as required (supplying step in themethod of manufacturing a nanotube-polymer composite of the presentinvention); and chemically bonding the functional groups together toform a cross-linked site (cross-linking step in the method ofmanufacturing a nanotube-polymer composite of the present invention). Insupplying the base body surface with the multiple carbon nanotubes towhich functional groups are bonded, the base body surface is preferablysupplied with a solution (cross-linking solution) containing the carbonnanotubes and a solvent. In particular, the solution is preferablyapplied as a cross-linking application solution to form a cross-linkedsubstance film, for simple formation of the nanotube-polymer compositeof the present invention at a low cost and in a short period of time.

(Other Additive)

The cross-linking solution (used in both the first method and the secondmethod) may contain various additives including a solvent, a viscositymodifier, a dispersant, and a cross-linking accelerator. A solvent isadded when satisfactory applicability of the cross-linking solution isnot achieved with the cross-linking agent or the additive for bondingthe functional groups alone. A solvent that can be employed is notparticularly limited, and may be appropriately selected according to thetype of the cross-linking agent or the additive for bonding thefunctional groups. Specific examples of such a solvent include: organicsolvents such as methanol, ethanol, isopropanol, n-propanol, butanol,methyl ethyl ketone, toluene, benzene, acetone, chloroform, methylenechloride, acetonitrile, diethyl ether, and tetrahydrofuran (THF); water;acidic aqueous solutions; and alkaline aqueous solutions. A solvent assuch is added in an amount that is not particularly limited butdetermined appropriately by taking into consideration the applicabilityof the cross-linking solution.

A viscosity modifier is also added when sufficient applicability is notachieved with the cross-linking agent or the additive for bonding thefunctional groups alone. A viscosity modifier that can be employed isnot particularly limited, and may be appropriately selected according tothe type of cross-linking agent or the additive for bonding thefunctional groups. Specific examples of such a viscosity modifierinclude methanol, ethanol, isopropanol, n-propanol, butanol, methylethyl ketone, toluene, benzene, acetone, chloroform, methylene chloride,acetonitrile, diethyl ether, and THF.

Some of those viscosity modifiers serve as a solvent when added in acertain amount, but it is meaningless to clearly distinguish theviscosity modifier from the solvent. A viscosity modifier as such isadded in an amount that is not particularly limited but determinedappropriately by taking into consideration the applicability.

A dispersant is added in order to maintain the dispersion stability ofthe carbon nanotubes, the cross-linking agent, or the additive forbonding the functional groups in the cross-linking solution. Variousknown surfactants, water-soluble organic solvents, water, acidic aqueoussolutions, alkaline aqueous solutions, etc. can be employed as adispersant. However, in the present invention, a dispersant is notalways necessary since components of the cross-linking solutionthemselves have high dispersion stability. In addition, depending on theuse of the final nanotube-polymer composite of the present invention,the presence of impurities such as a dispersant in the carbon nanotubestructure may not be desirable. In such a case, a dispersant is notadded at all, or is added in a very small amount.

The content of the cross-linking agent or additive for bonding thefunctional groups in the cross-linking solution varies depending on thetype of cross-linking agent (including whether the cross-linking agentis self-polymerizable or not self-polymerizable) or additive for bondingfunctional groups. The content also varies depending on the length andthickness of carbon nanotubes, whether single-wall carbon nanotubes ormulti-wall carbon nanotubes are used, the type and amount of functionalgroups in the carbon nanotubes, the presence or absence of a solvent orother additive used and, if one is used, the type and amount of thesolvent or additive, etc. Therefore, the content cannot be determineduniquely. In particular, for example, glycerin or ethylene glycol canalso provide characteristics of a solvent because a viscosity ofglycerin or ethylene glycol is not so high, and thus an excessive amountof glycerin or ethylene glycol can be added.

<Method of Preparing Cross-linking Solution>

A method of preparing a cross-linking solution is described next. Thecross-linking solution is prepared by mixing carbon nanotubes that havefunctional groups with a cross-linking agent that prompts across-linking reaction with the functional groups or an additive forbonding functional groups (mixing step). The mixing step may be precededby an addition step in which the functional groups are introduced intothe carbon nanotubes.

Use of carbon nanotubes having functional groups as starting materialsstarts the preparation from the mixing step. The use of normal carbonnanotubes themselves as starting materials starts the preparation fromthe addition step.

(Addition Step)

The addition step is a step of introducing desired functional groupsinto carbon nanotubes. How functional groups are introduced variesdepending on the type of functional group and cannot be determineduniquely. One method involves adding a desired functional groupdirectly. Another method involves: introducing a functional group thatis easily added; and then substituting the whole functional group or apart thereof, or adding a different functional group to the formerfunctional group, in order to obtain the target functional group. Stillanother method involves applying a mechanochemical force to a carbonnanotube to break or modify a very small portion of a graphene sheet onthe surface of the carbon nanotube, to thereby introduce variousfunctional groups into the broken or modified portion.

Furthermore, functional groups can be relatively easily introduced intocup-stacked carbon nanotubes, which have many defects on the surfaceupon manufacture, and carbon nanotubes that are formed by vapor phasegrowth. On the other hand, carbon nanotubes each having a perfectgraphene sheet structure exert the carbon nanotube characteristics moreeffectively and the characteristics are easily controlled. Consequently,it is particularly preferable to use a multi-wall carbon nanotube sothat an appropriate number of defects are formed on its outermost layeras a nanotube-polymer composite to bond functional groups forcross-linking while the inner layers having less structural defectsexert the carbon nanotube characteristics.

Operations for the addition step are not particularly limited, and anyknown method can be employed. Various addition methods disclosed in JP2002-503204 A may be employed in the present invention depending on thepurpose. A description is given on a method of introducing —COOR (In theformula, R represents a substituted or unsubstituted hydrocarbon group.R is preferably selected from —C_(n)H_(2n−1) and —C_(n)H_(2n+1) (nrepresents an integer of 1 to 10). Of those, a methyl group or an ethylgroup is more preferable.), a particularly desirable functional groupamong the functional groups listed above. To introduce —COOR (where Rrepresents a substituted or unsubstituted hydrocarbon group) into carbonnanotubes, carboxyl groups may be added to the carbon nanotubes once(1), and then esterified (2).

(1) Addition of Carboxyl Group

To introduce carboxyl groups into carbon nanotubes, carboxyl groups arerefluxed together with an acid having an oxidizing effect. Thisoperation is relatively easy and is preferable since carboxyl groupswith high reactivity can be added to carbon nanotubes. A briefdescription of the operation is given below.

Examples of an acid having an oxidizing effect include concentratednitric acid, a hydrogen peroxide solution, a mixture of sulfuric acidand nitric acid, and aqua regia. Concentrated nitric acid isparticularly used in concentration of preferably 5 mass % or higher,more preferably 60 mass % or higher.

A normal reflux method can be employed. The reflux temperature ispreferably close to the boiling point of the acid used. Whenconcentrated nitric acid is used, for instance, the temperature ispreferably set to 120° C. to 130° C. The reflux preferably lasts for 30minutes to 20 hours, more preferably for 1 hour to 8 hours.

Carbon nanotubes to which carboxyl groups are added (carbon nanotubecarboxylic acid) are produced in the reaction liquid after the reflux.The reaction liquid is cooled down to room temperature and then issubjected to a separation operation or washing as required, therebyobtaining the target carbon nanotube carboxylic acid.

(2) Esterification

The target functional group —COOR (where R represents a substituted orunsubstituted hydrocarbon group and a preferable R is such as thatdescribed above) can be introduced by adding an alcohol to the obtainedcarbon nanotube carboxylic acid and dehydrating the mixture foresterification.

The alcohol used for the esterification is determined according to R inthe formula of the functional group. That is, if R is CH₃, the alcoholis methanol, and if R is C₂H₅, the alcohol is ethanol. A catalyst isgenerally used in the esterification, and a conventionally knowncatalyst such as sulfuric acid, hydrochloric acid, or toluenesulfonicacid can be used in the present invention. The use of sulfuric acid as acatalyst is preferable from the viewpoint of not prompting a sidereaction in the present invention.

The esterification may be conducted by adding an alcohol and a catalystto carbon nanotube carboxylic acid and refluxing the mixture at anappropriate temperature for an appropriate time period. A temperaturecondition and a time period condition in this case depend on type ofcatalyst, type of alcohol, or the like and cannot be determineduniquely, but a reflux temperature is preferably close to the boilingpoint of the alcohol used. The reflux temperature is preferably in therange of 60° C. to 70° C. for methanol, for example. Further, a refluxtime period is preferably in the range of 1 to 20 hours, more preferablyin the range of 4 to 6 hours.

A carbon nanotube with the functional group —COOR (where R represents asubstituted or unsubstituted hydrocarbon group and a preferable R issuch as that described above) added can be obtained by separating areaction product from a reaction liquid after esterification and washingthe reaction product as required.

(Mixing Step)

The mixing step is a step of mixing, as required, carbon nanotubeshaving functional groups with a cross-linking agent prompting across-linking reaction with the functional groups or an additive forbonding the functional groups, to thereby prepare the cross-linkingsolution. In the mixing step, other components described in theaforementioned section titled [Nanotube-polymer Composite] are mixed, inaddition to the carbon nanotubes having functional groups and thecross-linking agent. Then, an amount of a solvent or a viscositymodifier is preferably adjusted considering applicability, to therebyprepare the cross-linking solution (cross-linking application solution)just before supply (application) to the base body.

Simple stirring with a spatula and stirring with a stirrer of a stirringblade type, a magnetic stirrer, and a stirring pump may be used.However, to achieve higher degree of uniformity in dispersion of thecarbon nanotubes to enhance storage stability while fully extending anetwork structure by cross-linking of the carbon nanotubes, anultrasonic disperser or a homogenizer may be used for powerfuldispersion. However, the use of a stirring device with a strong shearforce of stirring such as a homogenizer may cut or damage the carbonnanotubes in the solution, thus the device may be used for a very shortperiod of time.

A carbon nanotube structure is formed by supplying the base body surfacewith the cross-linking solution described above and curing thecross-linking solution. A supplying method and a curing method aredescribed in detail in the section below titled [Method of ManufacturingNanotube-polymer Composite].

The carbon nanotube structure in the present invention is in a state inwhich carbon nanotubes are networked. In detail, the carbon nanotubestructure is cured into a matrix form in which carbon nanotubes areconnected to each other through cross-linked sites, thereby sufficientlyexerting the characteristics of a carbon nanotube itself such as hightransmission characteristics. In other words, the carbon nanotubestructure has carbon nanotubes that are tightly connected to each other,contains no other binders and the like, and is thus composedsubstantially only of carbon nanotubes, so that characteristics peculiarto a carbon nanotube are used fully.

A thickness of the carbon nanotube structure of the present inventioncan be widely selected from being very thin to being thick according tothe use. Lowering a content of the carbon nanotubes in the cross-linkingsolution used (simply, lowering the viscosity by diluting) and applyingthe cross-linking solution as a thin film provide a very thin coat.Similarly, raising a content of the carbon nanotubes provides a thickcoat. Further, repeating the application provides an even thicker coat.A very thin coat from a thickness of about 10 nm can be formed, and athick coat without an upper limit can be formed through recoating. Apossible film thickness with one coating is about 5 μm. Further, a coatmay have a desired shape by pouring the cross-linking applicationsolution having a content or the like adjusted into a mold and bonding.

In forming the carbon nanotube structure according to the first method,a site where the carbon nanotubes are mutually cross-linked, that is,the cross-linked site formed through a cross-linking reaction betweenthe functional groups of the carbon nanotubes and the cross-linkingagent has a cross-linking structure. In the cross-linking structure,residues of the functional groups remaining after the cross-linkingreaction are connected together with a connecting group, which is aresidue of the cross-linking agent remaining after the cross-linkingreaction.

As described, the cross-linking agent, which is a component of thecross-linking solution, is preferably not self-polymerizable. A nonself-polymerizable cross-linking agent provides the finally formedcarbon nanotube structure constructed from a residue of only onecross-linking agent. The gap between the carbon nanotubes to becross-linked can be controlled to a size of a residue of thecross-linking agent used, thereby providing a desired network structureof the carbon nanotubes with high duplicability. Further, multiplecross-linking agents are not present between the carbon nanotubes, thusenabling enhancement of an actual density of the carbon nanotubes in thecarbon nanotube structure. Further, reducing a size of a residue of thecross-linking agent can extremely narrow a gap between each of thecarbon nanotubes both electrically and physically (carbon nanotubes aresubstantially in direct contact with each other).

Formation of the carbon nanotube structure with a cross-linking solutionprepared by selecting a single functional group of the carbon nanotubesand a single non self-polymerizable cross-linking agent results in thecross-linked site of the layer having an identical cross-linkingstructure (Case 1). Further, formation of the carbon nanotube structurewith a cross-linking solution prepared by selecting even multiple typesof functional groups of the carbon nanotubes and/or multiple types ofnon self-polymerizable cross-linking agents results in the cross-linkedsites of the layer mainly having a cross-linking structure based on acombination of the functional group and the non self-polymerizablecross-linking agent mainly used (Case 2).

In contrast, formation of the carbon nanotube structure with across-linking solution prepared by selecting self-polymerizablecross-linking agents, without regard to whether the functional groups ofthe carbon nanotubes and the cross-linking agents are of single ormultiple types, results in the cross-linked sites in the carbon nanotubestructure where carbon nanotubes are cross-linked together without amain, specific cross-linking structure. This is because the cross-linkedsites will be in a state where numerous connecting groups with differentconnecting (polymerization) numbers of the cross-linking agents coexist.

In other words, by selecting non self-polymerizable cross-linkingagents, the cross-linked sites, where the carbon nanotubes of the carbonnanotube structure cross-link together, have a mainly identicalcross-linking structure because a residue of only one cross-linkingagent bonds with the functional groups. “Mainly identical” here is aconcept including a case where all of the cross-linked sites have anidentical cross-linking structure as described above (Case 1), as wellas a case where the cross-linking structure based on a combination ofthe functional group and the non self-polymerizable cross-linking agentmainly used becomes a main structure with respect to the totalcross-linked sites as described above (Case 2).

When referring to “mainly identical”, a “ratio of identical cross-linkedsites” with respect to the total cross-linked sites will not have auniform lower limit defined. The reason is that a case of giving afunctional group or a cross-linking structure with an aim different fromformation of a carbon nanotube network may be assumed, for example.However, in order to realize high electrical or physical characteristicspeculiar to carbon nanotubes with a strong network, a “ratio ofidentical cross-linked sites” with respect to the total cross-linkedsites is preferably 50% or more, more preferably 70% or more, furthermore preferably 90% or more, and most preferably 100%, based on numbers.Those number ratios can be determined through, for example, a method ofmeasuring an intensity ratio of an absorption spectrum corresponding tothe cross-linking structure with an infrared spectrum.

As described, a carbon nanotube structure having the cross-linked sitewith a mainly identical cross-linking structure where carbon nanotubescross-link together allows formation of a uniform network of the carbonnanotubes in a desired state. In addition, the carbon nanotube networkcan be constructed with homogeneous, satisfactory, and expectedelectrical or physical characteristics and high duplicability.

Further, the connecting group preferably contains hydrocarbon as askeleton thereof. “Hydrocarbon as a skeleton” here refers to a mainchain portion of the connecting group consisting of hydrocarbon, themain portion of the connecting group contributing to connecting togetherresidues of the functional groups of carbon nanotubes to be cross-linkedremaining after a cross-linking reaction. A side chain portion, wherehydrogen of the main chain portion is substituted by anothersubstituent, is not considered. Obviously, it is more preferable thatthe whole connecting group consists of hydrocarbon.

The hydrocarbon preferably has 2 to 10 carbon atoms, more preferably 2to 5 carbon atoms, and further more preferably 2 to 3 carbon atoms. Theconnecting group is not particularly limited as long as the connectinggroup is divalent or more.

In the cross-linking reaction of the functional group —COOR (where Rrepresents a substituted or unsubstituted hydrocarbon group, and apreferable R is such as that described above) and ethylene glycol,exemplified as a preferable combination of the functional group ofcarbon nanotubes and the cross-linking agent, the cross-linked sitewhere multiple carbon nanotubes are mutually cross-linked becomes—COO(CH₂)₂OCO—.

Further, in the cross-linking reaction of the functional group —COOR(where R represents a substituted or unsubstituted hydrocarbon group,and a preferable R is such as that described above) and glycerin, thecross-linked site where multiple carbon nanotubes are mutuallycross-linked becomes —COOCH₂CHOHCH₂OCO— or —COOCH₂CH(OCO—)CH₂OH if twoOH groups contribute to the cross-linking, and the cross-linked sitebecomes —COOCH₂CH(OCO—)CH₂OCO— if three OH groups contribute to thecross-linking.

As has been described, in the nanotube-polymer composite of the presentinvention, the carbon nanotube structure formed through the first methodhas a network structure composed of multiple carbon nanotubes connectedto each other through multiple cross-linked sites. Thus, contact orarrangement of carbon nanotubes remains stable, unlike a mere carbonnanotube dispersion film. Therefore, the carbon nanotube structurestably exerts characteristics peculiar to carbon nanotubes including:electrical characteristics such as high electron- or hole-transmissioncharacteristics; physical characteristics such as thermal conductivityand toughness; and light absorption characteristics.

On the other hand, in forming the carbon nanotube structure through thesecond method, a site where the multiple carbon nanotubes are mutuallycross-linked, that is, a cross-linked site formed by a cross-linkingreaction among the functional groups of the multiple carbon nanotubeshas a cross-linking structure in which residues of the functional groupsremaining after a cross-linking reaction are connected to each other. Inthis case as well, the carbon nanotube structure has carbon nanotubesconnected to each other through a cross-linked site in a matrix form,thereby easily exerting the characteristics of carbon nanotubes itselfsuch as high electron- and hole-transmission characteristics. That is,the carbon nanotube structure has carbon nanotubes that are tightlyconnected to each other, contains no other binders and the like, and isthus composed substantially only of carbon nanotubes.

Further, the cross-linked sites are formed through directly reacting thefunctional groups with each other, thus enabling enhancement of theactual density of the carbon nanotubes of the carbon nanotube structure.Further, reducing a size of a functional group can extremely narrow agap between each of the carbon nanotubes both electrically andphysically, thereby easily exerting the characteristics of the carbonnanotube itself.

Further, cross-linked sites are formed by chemical bonding of thefunctional groups together, and thus, the carbon nanotube structure hasa mainly identical cross-linking structure. Therefore, a uniform networkof carbon nanotubes can be formed into a desired state. Further, thecarbon nanotube structure can be constructed with homogeneous,satisfactory, and expected electrical and physical characteristics andhigh duplicability.

A layer of other than the carbon nanotube structure may be formed in thecomposite of the present invention. For example, placing an adhesivelayer between the base body surface and the carbon nanotube structurefor enhancing adhesiveness therebetween is preferable for improving theadhesive strength of the carbon nanotube structure. A method of formingan adhesive layer and other details will be explained in the sectiontitled [Method of Manufacturing Nanotube-polymer Composite].

A specific shape and the like of the above-described nanotube-polymercomposite of the present invention will be made clear in the followingsection titled [Method of Manufacturing Nanotube-polymer Composite].Note that the descriptions below show merely examples and are not tolimit specific aspects of the nanotube-polymer composite of the presentinvention.

[Method of Manufacturing Nanotube-polymer Composite]

A method of manufacturing a composite of the present invention is amethod suitable for manufacturing the nanotube-polymer composite of thepresent invention described above. Specifically, the method includes:(A) a supplying step of supplying a base body with a solution(cross-linking solution) containing multiple carbon nanotubes havingfunctional groups; (B) a cross-linking step of mutually cross-linkingthe multiple carbon nanotubes through chemical bonding of the functionalgroups together to form a carbon nanotube structure having a networkstructure; (C) an impregnating step of impregnating the networkstructure with a polymer liquid; and (D) a combining step of combiningthe carbon nanotube structure and the polymer by curing the polymerliquid.

Hereinafter, details of the respective steps in the method ofmanufacturing a nanotube-polymer composite of the present invention willbe described.

(A) Supplying Step

In the present invention, the “supplying step” is a step of supplying asurface of a base body such as a slide glass with a solution containingcarbon nanotubes having functional groups.

The supplying method is not particularly limited, and any method can beadopted from a wide variety of methods to apply the cross-linkingsolution (cross-linking application solution) to the base body surface.For example, the solution may be simply dropped or spread with asqueegee or may be applied through a common application method on thebase body. Examples of common application methods include spin coating,wire bar coating, cast coating, roll coating, brush coating, dipcoating, spray coating, and curtain coating.

(B) Cross-linking Step

In the present invention, the “cross-linking step” is a step of formingthe carbon nanotube structure 1 (FIG. 1) having a net work structure bymutually cross-linking the multiple carbon nanotubes through chemicalbonding of the functional groups after supplying the cross-linkingsolution.

An operation carried out in the cross-linking step is naturallydetermined according to the combination of the functional groups andcross-linking agent or additive for bonding the functional groupstogether. A combination of thermosetting functional groups andcross-linking agent employs heating the cross-linking solution withvarious heaters or the like. A combination of functional groups and across-linking agent that are cured by UV rays employs irradiating thecross-linking solution with a UV lamp or leaving the cross-linkingsolution under the sun. A combination of air setting functional groupsand cross-linking agent only employs letting the cross-linking solutionstand still. “Letting the cross-linking solution stand still” is deemedas one of the operations that may be carried out in the cross-linkingstep of the present invention.

Heat curing (polyesterification through an ester exchange reaction) isconducted for the case of a combination of a carbon nanotube, to whichthe functional group —COOR (where R represents a substituted orunsubstituted hydrocarbon group and a preferable R is such as thatdescribed above) is added, and a polyol (among them, glycerin and/orethylene glycol). Heating causes an ester exchange reaction between—COOR of the esterified carbon nanotube carboxylic acid and R′—OH (whereR′ represents a substituted or unsubstituted hydrocarbon group) of thepolyol. As the reaction progresses multilaterally, the carbon nanotubesare cross-linked until a network of carbon nanotubes connected to eachother constructs a carbon nanotube structure 1.

To give an example of conditions preferable for the above combination,the heating temperature is specifically set to preferably 50° C. to 500°C., more preferably 150° C. to 200° C. The heating time period for theabove combination is specifically set to preferably 1 minute to 10hours, more preferably 1 to 2 hours.

(C) Impregnating Step

In the present invention, the “impregnating step” is a step of providingthe nanotube structure with a polymer liquid by dropping the polymerliquid onto the nanotube structure or immersing the nanotube structurein the polymer liquid.

(D) Combining Step

The nanotube-polymer composite is formed by impregnating the carbonnanotube structure 1 with the polymer liquid and then curing the polymerliquid through polymerization or the like of a polymer. A polymerizationmethod for the polymer liquid may employ a known method of manufacturinga polymer as appropriate according to the polymer liquid used as a rawmaterial. Any method of combining a polymer with a nanotube structuremay be employed as long as the method provides a composite having astructure shown in FIG. 1, and examples of the method further include amethod of dispersing a nanotube structure in a polymer liquid and thenapplying the dispersion to a base body. The obtained nanotube-polymercomposite has a structure of the nanotube structure 1 filled in thepolymer 2.

Hereinafter, the present invention will be described more specificallyby way of examples. However, the present invention is not limited to thefollowing examples.

EXAMPLE 1 Nanotube-polymer Composite Employing Glycerin Cross-linkedMulti-wall Carbon Nanotube Structure

(A) Supplying Step

(Addition Step)

30 mg of multi-wall carbon nanotube powder (purity: 90%, averagediameter: 30 nm, average length: 3 μm, available from ScienceLaboratories, Inc.) was added to 20 ml of concentrated nitric acid (60mass % aqueous solution, available from Kanto Kagaku) for reflux at 120°C. for 20 hours, to synthesize carbon nanotube carboxylic acid. Areaction scheme of the above is shown in FIG. 2. In FIG. 2, a carbonnanotube (CNT) portion is represented by two parallel lines (the sameapplies for other figures relating to reaction schemes).

The temperature of the solution was returned to room temperature, andthe solution was centrifuged at 5,000 rpm for 15 minutes to separate asupernatant liquid from a precipitate. The recovered precipitate wasdispersed in 10 ml of pure water, and the dispersion liquid wascentrifuged again at 5,000 rpm for 15 minutes to separate a supernatantliquid from a precipitate (the above process constitutes one washingoperation). This washing operation was repeated five more times, andfinally, a precipitate was recovered.

<Esterification>

30 mg of the carbon nanotube carboxylic acid prepared in the above stepwas added to 25 ml of methanol (available from Wako Pure ChemicalIndustries, Ltd.). Then, 5 ml of concentrated sulfuric acid (98 mass %,available from Wako Pure Chemical Industries, Ltd.) was added to themixture, and the whole was refluxed at 65° C. for 4 hours for methylesterification. The reaction scheme is shown in FIG. 3.

After the temperature of the solution had been returned to roomtemperature, the solution was filtered to separate a precipitate. Theprecipitate was washed with water, and was then recovered.

(Mixing Step)

10 mg of the carbon nanotube carboxylic acid methyl esterified in theabove step was added to 5 ml of glycerin (available from Kanto Kagaku),and the whole was mixed using an ultrasonic disperser. Further, themixture was added to 10 ml of methanol as a viscosity modifier.

(Applying Step)

About 0.1 ml of the obtained cross-linking application solution wasdropped and applied onto an SiO₂/Si substrate with a Pasteur's pipette.

(B) Cross-linking Step

As described above, the substrate to which the cross-linking applicationsolution of Example 1 was applied was heated at 200° C. for 2 hours forpolymerization through an ester exchange reaction, thereby forming anetwork structure (carbon nanotube structure) The reaction scheme isshown in FIG. 4.

(C) Impregnating Step

The obtained carbon nanotube structure was impregnated with a polyimideresin (Rikacoat PN-20, available from New Japan Chemical Co., Ltd.) bydropping about 0.1 ml of the resin.

(D) Combining Step

The substrate was heated at 200° C. for 20 minutes to cure the resin,thereby providing a nanotube-polyimide resin composite.

EXAMPLE 2

The carbon nanotube structure obtained in the same manner as in Example1 was impregnated with an epoxy resin (Araldite, available from CibaSpecialty Chemicals, Switzerland) by dropping and curing about 0.1 ml ofthe epoxy resin, thereby providing a nanotube-epoxy resin composite.

Carbon nanotubes are known to burn off when a large current is passedtherethrough in an atmosphere containing oxygen, and there is an upperlimit to a current that can be passed through the carbon nanotubes, thatis, to a current density in an atmosphere containing oxygen. However,the composite of the polymer and the nanotube structure of the presentinvention can shield the nanotube from oxygen and can raise the upperlimit of the current density, thereby providing a nanotube-polymercomposite capable of passing through a larger current. Further, bendingstrength of each nanotube-polymer composite was enhanced compared tothat of the resin alone, preventing breaking by bending.

1. A method of manufacturing a composite, comprising the steps in theorder of: applying a solution to a base body surface, wherein thesolution contains multiple carbon nanotubes to which multiple functionalgroups are bonded and may further contain additional substances; curingthe solution, thereby mutually cross-linking the multiple carbonnanotubes through either direct chemical bonds formed among the multiplefunctional groups, or by cross-linking the multiple functional groupstogether through a cross-linking agent, in order to construct a networkstructure of cross-linked carbon nanotubes that forms a cross-linkedsubstance film on the base body surface; impregnating the networkstructure with a polymer liquid; and curing the polymer liquidimpregnated in the network structure to form a nanotube-polymercomposite, wherein a reaction that forms the chemical bonding comprisesa substitution reaction for chemically bonding the multiple functionalgroups together, and the solution further contains an additivecomprising a base selected from the group consisting of sodiumhydroxide, potassium hydroxide, pyridine, and sodium ethoxide that formsthe chemical bonding of the multiple functional groups together.
 2. Amethod of manufacturing a composite according to claim 1, wherein theimpregnating step comprises dispersing the carbon nanotube structure inthe polymer liquid and curing the polymer liquid impregnated in thenetwork structure to form a nanotube-polymer composite.
 3. A method ofmanufacturing a composite according to claim 1, wherein the polymercomprises one polymer selected from the group consisting ofpolyethylene, polypropylene, polyvinyl chloride, polyamide, polyimide,and an epoxy resin.
 4. A method of manufacturing a composite accordingto claim 1, wherein: the solution contains a cross-linking agent thatcross-links the multiple functional groups together; and thecross-linking agent is not self-polymerizable.
 5. A method ofmanufacturing a composite according to claim 4, wherein: each of thefunctional groups comprises at least one functional group selected fromthe group consisting of —OH, —COOH, —COOR (where R represents asubstituted or unsubstituted hydrocarbon group), —COX (where Xrepresents a halogen atom), —NH₂, and —NCO; and the cross-linking agentis capable of prompting a cross-linking reaction with the selectedfunctional group.
 6. A method of manufacturing a composite according toclaim 4, wherein: the cross-linking agent comprises at least onecross-linking agent selected from the group consisting of a polyol, apolyamine, a polycarboxylic acid, a polycarboxylate, a polycarboxylicacid halide, a polycarbodiimide, and a polyisocyanate; and each of thefunctional groups is capable of prompting a cross-linking reaction withthe selected cross-linking agent.
 7. A method of manufacturing acomposite according to claim 4, wherein: each of the functional groupscomprises at least one functional group selected from the groupconsisting of —OH, —COOH, —COOR (where R represents a substituted orunsubstituted hydrocarbon group), —COX (where X represents a halogenatom), —NIH₂, and —NCO; the cross-linking agent comprises at least onecross-linking agent selected from the group consisting of a polyol, apolyamine, a polycarboxylic acid, a polycarboxylate, a polycarboxylicacid halide, a polycarbodiimide, and a polyisocyanate; and a combinationof the selected functional group and the selected cross-linking agent iscapable of prompting a mutual cross-linking reaction.
 8. A method ofmanufacturing a composite according to claim 5, wherein each of thefunctional groups comprises —COOR (where R represents a substituted orunsubstituted hydrocarbon group).
 9. A method of manufacturing acomposite according to claim 8, wherein the crosslinking agent comprisesa polyol.
 10. A method of manufacturing a composite according to claim9, wherein the cross-linking agent comprises at least one selected fromthe group consisting of glycerin, ethylene glycol, butenediol,hexynediol, hydroquinone, and naphthalenediol.
 11. A method ofmanufacturing a composite according to claim 1, wherein the solutionfurther contains a solvent.
 12. A method of manufacturing a compositeaccording to claim 11, wherein the cross-linking agent also serves as asolvent.
 13. A method of manufacturing a composite according to claim 1,wherein each of the functional groups comprises one functional groupselected from the group consisting of —NH₂, —X (where X represents ahalogen atom), —SH, —OH, —OSO₂CH₃, and —OSO₂(C₆H₄)CH₃.
 14. A method ofmanufacturing a composite comprising the steps in the order of: applyinga solution to a base body surface, wherein the solution containsmultiple carbon nanotubes to which multiple functional groups are bondedand may further contain additional substances; curing the solution,thereby mutually cross-linking the multiple carbon nanotubes througheither direct chemical bonds formed among the multiple functionalgroups, or by cross-linking the multiple functional groups togetherthrough a cross-linking agent, in order to construct a network structureof cross-linked carbon nanotubes that forms a cross-linked substancefilm on the base body surface; impregnating the network structure with apolymer liquid; and curing the polymer liquid impregnated in the networkstructure to form a nanotube-polymer composite, wherein a reaction thatforms the chemical bonding comprises an oxidative reaction forchemically bonding the multiple functional groups together, and thesolution further contains an oxidative reaction accelerator comprisingiodine.
 15. A method of manufacturing a composite according to claim 14,wherein each of the functional groups comprises —SH.
 16. A method ofmanufacturing a composite according to claim 14, wherein theimpregnating step comprises dispersing the carbon nanotube structure inthe polymer liquid and curing the polymer liquid impregnated in thenetwork structure to form a nanotube-polymer composite.
 17. A method ofmanufacturing a composite according to claim 14, wherein the polymercomprises one polymer selected from the group consisting ofpolyethylene, polypropylene, polyvinyl chloride, polyamide, polyimide,and an epoxy resin.
 18. A method of manufacturing a composite accordingto claim 14, wherein: the solution contains a cross-linking agent thatcross-links the multiple functional groups together; and thecross-linking agent is not self-polymerizable.
 19. A method ofmanufacturing a composite according to claim 18, wherein: each of thefunctional groups comprises at least one functional group selected fromthe group consisting of —OH, —COOH, —COOR (where R represents asubstituted or unsubstituted hydrocarbon group), —COX (where Xrepresents a halogen atom), —NH₂, and —NCO; and the cross-linking agentis capable of prompting a cross-linking reaction with the selectedfunctional group.
 20. A method of manufacturing a composite according toclaim 18, wherein: the cross-linking agent comprises at least onecross-linking agent selected from the group consisting of a polyol, apolyamine, a polycarboxylic acid, a polycarboxylate, a polycarboxylicacid halide, a polycarbodiimide, and a polyisocyanate; and each of thefunctional groups is capable of prompting a cross-linking reaction withthe selected cross-linking agent.
 21. A method of manufacturing acomposite according to claim 18, wherein: each of the functional groupscomprises at least one functional group selected from the groupconsisting of —OH, —COOH, —COOR (where R represents a substituted orunsubstituted hydrocarbon group), —COX (where X represents a halogenatom), —Nib, and —NCO; the cross-linking agent comprises at least onecross-linking agent selected from the group consisting of a polyol, apolyamine, a polycarboxylic acid, a polycarboxylate, a polycarboxylicacid halide, a polycarbodiimide, and a polyisocyanate; and a combinationof the selected functional group and the selected cross-linking agent iscapable of prompting a mutual cross-linking reaction.
 22. A method ofmanufacturing a composite according to claim 19, wherein each of thefunctional groups comprises —COOR (where R represents a substituted orunsubstituted hydrocarbon group).
 23. A method of manufacturing acomposite according to claim 22, wherein the crosslinking agentcomprises a polyol.
 24. A method of manufacturing a composite accordingto claim 23, wherein the cross-linking agent comprises at least oneselected from the group consisting of glycerin, ethylene glycol,butenediol, hexynediol, hydroquinone, and naphthalenediol.
 25. A methodof manufacturing a composite according to claim 14, wherein the solutionfurther contains a solvent.
 26. A method of manufacturing a compositeaccording to claim 25, wherein the cross-linking agent also serves as asolvent.